Current measuring apparatus with redundant current measurement

Abstract

The invention relates to a current measuring apparatus for redundant measurement of an electric current (I) with a low-resistance current measuring resistor ( 1 ) for current measurement according to the four-lead technique and with a magnetic field sensor ( 14 ). The invention provides that the electric current (I) to be measured in the current measuring apparatus is divided into a main current path with a main current (I 1 ) and a secondary current path with a secondary current (I 2 ), the main current path and the secondary current path together forming a parallel circuit. The low-resistance current measuring resistor ( 1 ) is arranged in the main current path and has the main current (I 1 ) flowing through it, while the magnetic field sensor ( 14 ) is arranged in the secondary current path and measures the secondary current (I 2 ).

The invention claimed is: 
     
         1 . A current measuring apparatus for measuring an electric current, comprising:
 a) a low-resistance current measuring resistor for current measurement according to the four-wire technique, and   b) a magnetic field sensor, in particular as a Hall sensor or as a magnetoresistive magnetic field sensor, for redundant current measurement,   c) wherein the electric current to be measured is divided in the current measuring apparatus into a main current path with a main current and a secondary current path with a secondary current, the main current path and the secondary current path together forming a parallel circuit,   d) wherein the low-resistance current measuring resistor is arranged in the main current path and has the main current flowing through it, and   e) wherein the magnetic field sensor is arranged in the secondary current path and measures the secondary current,   f) wherein the parallel circuit is designed such that the main current through the main current path with the low-resistance current measuring resistor is greater than the secondary current in the secondary current path with the magnetic field sensor, namely by a factor of at least 10,   g) wherein the low-resistance current measuring resistor is plate-shaped, with plate-shaped current connecting parts and a plate-shaped resistor element, the plate-shaped resistor element being arranged between the two plate-shaped current connecting parts in the direction of current flow,   h) wherein
 a) a printed circuit board is arranged on the plate-shaped current measuring resistor, and 
 b) the printed circuit board makes contact with the two current connecting parts of the low-resistance current measuring resistor by means of in each case at least one through-plating, and 
 c) the magnetic field sensor is arranged on the printed circuit board, and 
 d) the magnetic field sensor on the one hand and the current measuring resistor on the other hand are arranged on opposite sides of the printed circuit board, and 
 e) a compensating resistor is arranged on the printed circuit board, and 
 f) the secondary current path runs on and/or in the printed circuit board, while the main current path runs through the low-resistance current measuring resistor, and 
 g) an evaluation circuit is arranged on the printed circuit board, which detects at least one of the following:
 g1) the voltage drop across the resistance element of the low-resistance current measuring resistor, 
 g2) the output signal of the magnetic field sensor, and 
 g3) the voltage drop across the compensating resistor in the secondary current path, 
 
 and 
 h) the evaluation circuit has an interface for outputting the output signal of the magnetic field sensor. 
   
     
     
         2 . A current measuring apparatus according to  claim 1 , wherein the secondary current path has an electrical resistance value which is greater than the resistance of the main current path by a factor of at least 10. 
     
     
         3 . A current measuring apparatus according to  claim 1 , wherein the low-resistance current measuring resistor has a larger current measuring range than the magnetic field sensor. 
     
     
         4 . A current measuring apparatus according to  claim 1 , wherein
 a) the compensating resistor is arranged in the secondary current path with the magnetic field sensor,   b) the compensating resistor is dimensioned with respect to its resistance value such that the temperature dependence of the resistance value of the conductor material is at least partially compensated for,   c) the main current path and the secondary current path each contain conductor material with a specific first temperature coefficient with respect to the resistance value and resistor material with a specific second temperature coefficient with respect to the resistance value.   
     
     
         5 . A current measuring apparatus according to  claim 4 , wherein the main current path and the secondary current path have the same resistance ratio between the resistance value of the conductor material and the resistance value of the resistor material with a deviation of less than ±20. 
     
     
         6 . A current measuring apparatus according to  claim 5 , wherein
 a) the first temperature coefficient of the conductor material is in the range of 1,000-10,000, and   b) the second temperature coefficient of the resistor material is in the range of 0 to ±100 ppm/K.   
     
     
         7 . A current measuring apparatus according to  claim 1 , wherein, at least one of the two plate-shaped current connecting parts of the low-resistance current measuring resistor has an incision on at least one side adapted for temperature compensation. 
     
     
         8 . A current measuring apparatus according to  claim 1 , wherein a plurality of voltage measuring contacts are arranged on the plate-shaped current connecting parts of the low-resistance current measuring resistor. 
     
     
         9 . A current measuring apparatus according to  claim 1 , wherein,
 a) the printed circuit board has several layers,   b) the compensating resistor is arranged on the uppermost layer of the printed circuit board,   c) the secondary current path upstream of the compensating resistor is divided among a plurality of layers of the printed circuit board,   d) the secondary current path is brought together upstream of the compensating resistor on the uppermost layer of the printed circuit board and then runs completely through the compensating resistor on the uppermost layer of the printed circuit board, and   e) the secondary current path downstream of the compensating resistor is again divided into several layers of the printed circuit board.   
     
     
         10 . A current measuring apparatus according to  claim 4 , further comprising voltage measuring contacts for measuring the electrical voltage dropping across the compensating resistor for a current measurement according to the four-wire technique also in the secondary current path, so that the current measurement in the secondary current path is carried out both according to the four-wire technique and by the magnetic field sensor. 
     
     
         11 . A current measuring apparatus according to  claim 4 , wherein
 a) the current measuring apparatus has a high-voltage area and a low-voltage area,   b) the magnetic field sensor measures the secondary current on the input side in the high-voltage area, and   c) the magnetic field sensor outputs the output signal on the output side in the low-voltage area,   d) the compensating resistor is preferably arranged in the high-low-voltage area,   e) the magnetic field sensor preferably contains an insulation which insulates the low-voltage area from the high-voltage area.   
     
     
         12 . A current measuring apparatus according to  claim 1 , wherein
 a) the current measuring apparatus has a current measuring range that extends to at least 0.5, and   b) the current measuring apparatus permits an operating voltage of at least 100 V on the input side, and   c) the conductor material of the current connecting parts of the low-resistance current measuring resistor is copper or a copper alloy or aluminum or an aluminum alloy, and   d) the resistance material of the resistance element of the low-resistance current measuring resistor is selected from a group consisting of the following alloys:
 d1) a copper alloy, 
 d2) a nickel alloy, and 
   e) the conductor material of the current connecting parts of the low-resistance current measuring resistor has a lower specific electrical resistance than the resistance material of the resistance element of the low-resistance current measuring resistor, and   f) the resistive material of the resistor element of the low-resistance current measuring resistor has a specific electrical resistance of less than 1000 μΩcm, and   g) the conductor material of the current connecting parts of the low-resistance current measuring resistor has a specific electrical resistance of less than 20 μΩcm and   h) the low-resistance current measuring resistor has a resistance value which is at most 500 mΩ.   
     
     
         13 . A current measuring apparatus according to  claim 7 , wherein
 a) the first temperature coefficient of the conductor material is substantially greater than the second temperature coefficient of the resistor material, in particular by a factor of at least 10,   b) the compensating resistor in the secondary current path consists of a resistor material which has a substantially lower temperature coefficient than the conductor material.   
     
     
         14 . A current measuring apparatus according to  claim 10 , wherein at least one of the two plate-shaped current connecting parts has an incision in the center adapted for trimming the resistance value. 
     
     
         15 . A current measuring apparatus according to  claim 13 , wherein voltage measuring contacts are distributed transversely to the current flow direction. 
     
     
         16 . A current measuring apparatus according to  claim 14 or claim 8 , wherein the central incision in the plate-shaped current connecting part surrounds one of the voltage measuring contacts as a current shadow. 
     
     
         17 . A current measuring apparatus according to  claim 1 , wherein the main current is greater than the secondary current by a factor of at least 10. 
     
     
         18 . A current measuring apparatus according to  claim 1 , wherein the main current is greater than the secondary current by a factor of at least 100. 
     
     
         19 . A current measuring apparatus according to  claim 6 , wherein the current measuring range of the low-resistance current measuring resistor is larger than the current measuring range of the magnetic field sensor by a factor of at least 10. 
     
     
         20 . A current measuring apparatus according to  claim 1 , wherein the magnetoresistive magnetic field sensor is a GMR sensor. 
     
     
         21 . A current measuring apparatus according to  claim 1 , wherein
 a) the resistance value of the main current path lies in the range of 50 μΩ with a deviation of at most ±50%, and   b) the resistance value of the secondary current path lies in the range of 20 mΩ with a deviation of maximum ±50%.